1. Field of Invention
The present invention relates to a CMOS light sensor and the operation method thereof. More particularly, the present invention relates to a CMOS light sensor and operation method that uses segment processing.
2. Description of Related Art
Most light sensors are classified into two major types, a charge-coupled device (CCD) or a CMOS light sensor. In a conventional CCD sensor, each light sensing line is assigned a group of shift registers for holding the charges produced by the CCD sensing line. In general, the amount of charges produced by the CCD sensor depends on the strength of illumination. Once the charges are fully transferred to the shift registers, the charges are sequentially shifted away from the shift registers to the circuit in the next processing stage. Similarly, as shown in FIG. 1, each CMOS light sensor 10 has a plurality of light sensing lines (12a, 14a and 16a) and each has a functional element similar to the shift register in the charge couple device. However, instead of shift registers, these functional elements are capacitors.
The structure of the CMOS light sensor 10 and the conventional CCD sensor are almost identical except the deployment of a capacitor in the former instead of a shift register. Hence, the method of operating the CMOS light sensor 10 is very similar to the method of operating the CCD sensor. The CMOS sensor 10 is exposed to light so that the sensing cells (such as 120a, 122a, 140a, 142a, 160a and 162a) in the light sensing lines (12a, 14a and 16a) generate an amount of electric charges in proportional to the intensity of illumination. Thereafter, various sensor cells (such as 120a, 122a, 136a and 138a) within the same light sensing line (such as 12a) are sampled individually to reproduce a corresponding electric potential. The capacitors within the aforementioned capacitor line (such as 12b) are actually storage device for registering the sampled electric potential.
In general, the capacitor line registers the resultant electric potentials produced by the entire light sensing line all at once but the electric potentials within the capacitor line are read out sequentially. Therefore, time to read out all of the potentials within the capacitor line increases with the number of sensor cells in a light sensing line. Since charge leakage occurs on most capacitors, the total number of charges drained away from the capacitor increases with time. If too many charges leak away from the capacitor, the actual stored data (electric potential) may be seriously distorted.